San Francisco Chronicle: We're driving north along the San Francisco waterfront in Toyota's new fuel-cell sedan when the smooth, rounded rear of a Tesla Motors Model S pulls into the lane in front of us. Like the Model S, Toyota's latest clean car runs on an electric motor - no gasoline required. Unlike the Model S, the sedan doesn't get its energy from a big battery pack. Instead, a hydrogen fuel cell beneath the front seats feeds a steady stream of electricity to the motor. The cars represent two different visions of...